1. Field of the Invention
This invention relates to a wet processing device and relates in particular to a wet processing device for washing with liquid, the wafer surface for forming into a semiconductor substrate.
2. Description of the Prior Art
In the prior art, washing of the wafer surface to form the semiconductor substrate for fabricating the semiconductor elements, utilized a wet processing device using a chemical such as sulfuric acid.
A cross sectional view of the chemical tank and a cross sectional view of the wash tank comprising the wet processing device for describing an example of the prior art are shown respectively in FIG. 5A and FIG. 5B. The wet processing device of the prior art, as shown in FIG. 5A and FIG. 5B is comprised of a chemical tank 1 consisting of an inner tank 1a filled with a chemical 5 such as sulfuric acid and an outer tank 1b formed on the periphery above the inner tank 1a, a wafer conveyor 8 for moving the wafer 2, and a wash tank 15 for washing the processed wafer 2.
As shown in FIG. 5A, when the inner tank 1a of the chemical tank 1 is filled with a chemical 5, a wafer stand 3 at the bottom is prepared, and a wafer 2 held by a conveyor chuck 9 of the wafer conveyor 8 are moved along the conveyor shaft 8a, and placed on the wafer stand 3. When loading of the wafer 2 is finished, the wafer conveyor 8 moving along with the conveyor shaft 8a, separates from the inner tank 1. The chemical tank 1 is also formed with an outer tank 1b on the upper part on the outer circumference and along with containing the chemical 5 such as sulfuric acid that overflowed from the inner tank 1a, also connects to a chemical line formed between the outer tank 1b and the inner tank 1a for circulating the chemical 15. A circulating pump 13 and a filter 14 are installed on this chemical line and fulfill the functions of circulating and filtering the chemical 5. In this way, when the surface processing of the wafer 2 is performed for a specified time inside the chemical tank 1, the dust particles that were attached to the wafer surface float free and are separated along with the air bubbles 4 within the chemical 5. When the processing within the chemical tank 1 is complete, the wafer conveyor 8 once again moves inside the chemical tank 1, holds the wafer 2 in the conveyor chuck 9 and extracts the wafer 2 from the chemical tank 1.
The wafer 2 extracted from the chemical tank 1 as shown in FIG. 5B is conveyed to the wash tank 15, and placed on the wafer stand 16 installed on the bottom of the wash tank 15 filled with distilled water. When placement of the wafer 2 is complete, the wafer conveyor 8 is pulled up to the outside, the same as in the case of the chemical tank 1. The wash tank 15 is connected to a water supply line 17 in the bottom, and an air-operated water supply valve 18 is installed in the water supply line 17. After supplying wash water for a specified time, the wafer 2 is once again pulled up on the wafer conveyor 8, and the wet processing is complete.
In other words, in the wet processing device of the prior art, a wafer 2 is conveyed to the chemical tank 1 by the wafer conveyor 8, and after a fixed amount of processing time, is lifted at a fixed speed from the chemical tank 1. The wafer 2 is then transported to the wash tank 15, the air-operated water supply valve 18 is opened, distilled water supplied from the water supply line 12 and washing performed.
The above described wet processing device of the prior art has the problems that the wafer can only be conveyed at the fixed pull-up speed set during the startup adjustment, and that the supply (filling) speed of the distilled water was also a fixed speed.
When for example the wafer was conveyed in a state with air bubbles in the chemical still remaining on the wafer surface, these residual air bubbles widened the surface area of the wafer so that dust particles in the air tended to easily adhere to the wafer surface. The device of the prior art therefore had the problem that many dust particles remained on the wafer after wet processing.
To avoid the problems caused by the effect of airborne particles and air bubbles, the pull-up speed of the wafer can be set to a high speed however at a fast pull-up speed, the quantity of chemical flowing into the wash tank becomes large, and the flow rate of distilled water into the wash tank must be set to a large amount. Therefore, in the wet processing device of the prior art, the pull-up speed had to be set to a fixed speed, and the supply of distilled water had to be fixed at large quantity.
Wafers however, have to actually be processed under various conditions. Some wafers tending to generate many air bubbles and some wafers tending to generate few bubbles are both present during the chemical processing. The wafers are also effected by the hydrogen peroxide concentration in the mixed solution of sulfuric acid and water.
Therefore, when a large quantity of water is constantly supplied in this way, to the wash tank while a mix of a large quantity of air bubbles and a small quantity of air bubbles are generated overall during the chemical processing, the prior art had the problem of an overly large cost for distilled water.
In view of the problems of the prior art, this invention has the object of providing a wet processing device capable of limiting the amount of distilled water usage in the chemical tank and wash tank, reducing the particle adherence to the wafer after wet processing caused by adherence of airborne dust and air bubbles remaining on the wafer surface after being raised from the chemical tank, handling various types of wafers, providing uniform wafer quality, and further improving the reliability of the product to a higher level.
To achieve the above objects, the wet processing device of this invention is comprised of a chemical processing tank to store chemicals for processing the surface of the wafer, a wafer conveyor to carry the wafer in and out of the interior of the chemical processing tank, a sensor to determine the amount of air bubbles occurring within the chemical when present within the chemical processing tank and issue a first and a second control signal, and a wash tank to store water for washing the wafer carried out from the chemical processing tank by the wafer conveyor. The rising speed of the wafer conveyor device pulling the wafer up from the chemical processing tank is controlled in response to the first control signal, and the wash tank water fill quantity for supplying water to the wash tank is controlled in response to the second control signal.